iMac caught in reboot loop. LED #3 flashes before reboot
Hi, My iMac is playing up and won't boot. I've pulled off the screen and notice that LED 1 & 2 are fine but LED 3 flashes on when the boot tone sounds then the computer resets. LED 4 never lights.
I've videoed the process here: https://youtu.be/RuACtKfZkMw
Any ideas what needs replacing?
All suggestions apprecited